Phenolic resin impregnated asbestos laminates are well known in the art, and taught, for example by Hood et al., in U.S. Pat. No. 3,018,206. Because of their wear resistance and lubricity, asbestos laminates had been used for many years as a rather unique material for rub strips, gaskets, and washers, in high temperature applications. A particularly useful application had been as a wear or rub strip, contacting the chain in the driving mechanisms in forced air textile drying ovens. These ovens operated at between about 150.degree. C. and 200.degree. C., where a high temperature strip material was required, which additionally would not cause excessive wear to the expensive contacting drive chain.
In this type of oven, sets of gears rotating about a vertical axis drive a set of parallel continuous chains, to which supported textile fabric is held therebetween. The "continuous chain" includs a metallic belt or chain used in some fashion to support and continuously pull, drive, or advance the fabric through the oven. The chain cannot be in complete tension, and so, at the middle point between its drawing gears it is displaced downward to some degree from the horizontal plane, where it comes into frictional contact with a supporting wear or rub strip disposed below it.
Various health problems however, have been attributed to asbestos fiber and a substitute is needed rub strips; additionally, asbestos provided a rather heavy substrate which could be impregnated with resin only up to a treated ratio of about 2.2, i.e., about 1.2 lb. of resin solids for each 1 lb. of asbestos.
Resin impregnated glass laminates, tried as an asbestos substitute, have been found very abrasive for rub strip applications. Resin impregnated woven Dacron polyethylene terephthalate cloth, provided a rather expensive, heavy laminate which could not be very highly loaded due to the structure of the weaving. Even brass has been tried, but it is expensive and very heavy. Polyethylene terephthalate in spun bond form has been used as an asbestos substitute in the manufacture of polyvinyl chloride coated, structured floor tiles, as taught by Kuhn et al., in U.S. Pat. No. 4,234,651. There, needled, spun bonded polyethylene glycol terephthalate fiber web had a thermoplastic, styrene-butadiene based binder applied thereto in an amount of up to about 30 wt.% binder solids relative to fiber. The binder was required, to provide high shear strength for the final product.
Plotz et al., in U.S. Pat. No. 3,967,032, also used a spun fleece of polyester monofilaments treated with a thermoplastic, butyl acrylate-styrene binder, containing from 10 wt.% to 30 wt.% of a melamine-formaldehyde precondensate, in an amount of up to about 30 wt.% binder solids relative to fiber. The binder was required, to provide high tensile and flexural strength for the bituminized roof sheet final product, and to solve shrinkage problems. Neither of these binder treated substrates with either polyvinyl chloride or bitumen coatings were directed to high temperature, lubricating laminates.